Process of making sodium cyanid.



UNITED STATES PATE T OFFICE.

FRITZ ROESSLER, OF FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR TO THEROESSLER & HASSLAOHER CHEMICAL COMPANY, OF NEW YORK,

N. Y., A FIRM.

PROCESS OF MAKING'SODIUM CYANIYD.I

SPECIFICATION forming part of Letters Patent N 0. 708,079, datedSeptember 2, 1902. Application filed February 4, 1899. Serial No.704,564. (ll specimens.)

To all whom it may concern.-

Be it known that I, FRITZ ROESSLER, a subject of the Emperor of Germany,and a resident of Frankfort-on-the-Main, Germany, have invented certainnew and useful Improvements in Processes of Making Sodium Oyanid, ofwhich the following is a specification.

The majority of methods for obtaining cyanids synthetically yield invariable proportions a mixture of charcoal, alkali cyanid, and alkalicarbonate, from which a marketable product is only derived bylixiviation, evaporation, and fusion. Numerous difficulties attend theseoperations. Lixiviating the mixture yields a lye which contains so muchcarbonate mixed with the cyanid that direct evaporation gives a productof low value. Moreover, it is known that cyanid solutions whenevaporated without a vacuum undergo decomposition. Complete evaporationto dryness in a vacuum is, however, rendered almost impossible, becausethe salt which separates forms a sticky mass on the floor of g thevessel, prohibiting agitation by means of stirrers. Furthermore, thisdeposit is a bad conductor of heat and so retards evaporation.

' Siepermanns method (D. R. P., No. 51,562) takes advantage of thedifference in solubility of potassium cyanid and potassium carbonate,the former being salted out from a warm concentrated solution by addingpotassium carbonate. The method is not applicable to the sodium salts,as the solubility relation- 3 5 ship is quite different. In synthesizingcyanids, however, the sodium salts offer a series of other advantagesover the potassium compounds which makes'it desirable to employ them.

The objects of the present method are to obtain from a mixture of sodiumcyanid and carbonate of soda in any proportions a sodium-- cyanid lyewhich is nearly free from sodium carbonate and to avoid completeevaporation 5 and the loss of cyanid which this involves and preparefrom this lye a pure anhydrous sodium cyanid which can be converteddirect into the marketable form by fusion.

The first part of the process depends on the fact not hitherto observedthat contrary to the behavior of the potassium salts the sodium cyanidprecipitates sodium carbonate from the lyes.

While a solution containing three hundred and twenty grams of sodiumcyanid (NaCy) I per liter is capable of dissolving sixty-five grams ofsodium carbonate, (Na CO 'a sodium-cyanid solution concentrated at 24centigrade (containing four hundred and twentyfour grams of NaOy perliter) only dissolves 6o forty-seven grams of Na OO a solutionconcentrated at 33 centigrade (with five hundred and seventeen grams ofNaOy per liter) dissolving only twenty-six grams of Na OO The maximumsolubility ot'csodium cyanid (five hundred and seventeen grams in oneliter of solution) is attained at 33 centigrade.

No further quantity of sodium cyanid dissolves on raising thetemperature. If, therefore, a mixture of sodium cyanid and carbonate ofsoda be treated with moderately-warm water in quantity insnfficient tocompletely dissolve the sodium cyanid, the maximum concentration shouldyield, according to the above data, a lye containing five hundred andseventeen grams of NaOy and twenty-six grams of Na,OO per liter. Asecond treatmentwith such a quantity of water as is necessary todissolve all the cyanid left in the Y massafter the first treatmentwould then yield a lye which contains the remainder of the NaOy and muchmore sodium carbonate than existed in the first lye. If this secondsolution be used for lixiviating'a fresh quantity of the mixture'of NaGyand Na OO a further amount of NaOy passes into solution, no Na OO beingdissolved, but rather a portion of the Na CO originally present in thelye is precipitated in proportion to the NaOy dissolved. On washing theresidue 0 there is obtained a lye which, being again poorer in cyanidand richer in carbonate, can

be used for extracting the subsequent portions. By systematic extractionat a moderate temperature it isin this manner possible 9 5 to obtainfrom a chance mixture of sodium cyanid and sodium carbonate a lyecontaining NaCy and Na CO in the proportion of one hundred to five. Thelye which has been concentrated in this manner yields on cool 10o ing acopious deposit of crystals consisting of NaOy-i-Qaq. These crystals canbe freed from water of crystallization by exposure to a vacuum atordinary temperatures over sulfuric acid or calcium chlorid. Thefollowing is a more rational method, depending on the fact, hithertounobserved, that if the crystals of NaGy+2aq are dissolved in theirWater of crystallization at 33 they do not yield a clear liquid.Fortyper cent. of NaOy which they contain separates as anhydrous salt,which is not redissolved on raising the temperature. The anhydrous saltseparates in a granular form and is quite easily freed from themother-liquid by suitable means. The latter solution again contains fivehundred and seventeen grants of NaCy per liter and deposits crystals ofNaGy-I-Laq on coolin The mother-liquors obtained in the crystallizationare used for dissolving fresh quantities of cyanid or concentrated in avacuum until containing five hundred and seventeen grams of NaCy perliter.

\Vhat I claim, and desire to secure by Letters latent, is

1. The method substantially as hereinbefore described of obtainingsodium cyanid, which consists in treating a mixture of sodium cyanid andsodium carbonate with insufficient water to dissolve the cyanidcompletely, forming a lye, separating the lye from the mixture, againtreating the remaining mixture with such a quantity of water as isnecessary to dissolve all the cyanid left in the mass after the firsttreatment forming a second lye, and lixiviating a fresh quantity of themixture of sodium cyanid and sodium carbonate with the second lye,whereby the sodium carbonate in the solution is displaced by sodiumcyanid, as and for the purposes set forth.

2. The method substantially as hereinbefore described of obtainingsodium cyanid, which consists in treating a mixture of sodium cyanid andsodium carbonate with insufiicient water to dissolve the cyanidcompletely, forming a lye, separating the lye from the mixture, againtreating the remaining mixture with such a quantity of water as isnecessary to dissolve all the cyanid left in the mass after the firsttreatment, forming a second lye, lixiviating a fresh quantity of themixture of sodium cyanid and sodium carbonate with the second lye,whereby the sodium carbonate in the solution is displaced by sodiumcyanid, and depositing crystals of sodium cyanid by cooling, as and forthe purposes set forth.

3. The method substantially as hereinbefore described of obtainingsodium cyanid, which consists in treating a mixture of sodium cyanid andsodium carbonate with insufficient water to dissolve the cyanidcompletely, forming a lye, separating the lye from the mixture, againtreating the remaining mixture with such a quantity of water as isnecessary to dissolve all the cyanid left in the mass after the firsttreatment, forming a second lye, lixiviating a fresh quantity of themixture of sodium cyanid and sodium carbonate with the second lye,whereby the sodium carbonate in the solution is displaced by sodiumcyanid, depositing crystals of sodium cyanid by cooling, and freeing thecrystals from their water of crystallization, as and for the purpose setforth.

4. The method substantially as hereinbefore described of obtainingsodium cyanid, which consists in treating a mixture of sodium cyanid andsodium carbonate with insufficient water to dissolve the cyanidcompletely, forming a lye, separating the lye from the mixture, againtreating the remaining mixture with such a quantity of water as isnecessary to dissolve all the cyanid left in the mass after the firsttreatment, forming a second lye, lixiviating a fresh quantity of themixture of sodium cyanid and sodium carbonate with the second lye,whereby the sodium carbonate in the solution is displaced by sodiumcyanid, depositing crystals of sodium cyanid by cooling, and fusing thecrystals of sodium cyanid in their water of crystallization at about 33centigrade, whereby the cyanid is separated in a state free from water,as and for the purpose set forth.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

FRITZ ROESSLER.

Witnesses:

PAUL MAUsoLFF, OTTO STRAUB.

